A vacuum pump has previously been disposed on the rear end portion of the electric generator for motor vehicles and the construction thereof will be described in conjunction with FIGS. 1 and 2.
A rear bracket (1) for an electric generator used with a motor vehicle supports a shaft (2) in a bearing (3) and the shaft is driven by an engine not shown. A rotor (4) is mounted to said shaft (2) by the spline fitting. A housing (5) has an inner cylindrical peripheral surface eccentric from the centers of said shaft (2) and said rotor (4), and a plate (6) closes the end of said housing (5) facing said rear bracket (1) and with said housing (5) forms a pump operating chamber (7). A mounting bolt (8) fixes said housing (5) and said plate (6) to said rear bracket (1). Vanes (9) are radially slidably mounted on said rotor (4). Packings (10) and (11) are provided for sealing the junctions between said rear bracket (1) and the plate (6) and between said plate (6) and the housing (5). An oil seal (12) is fixed to said bracket (1) and contacts the periphery of said shaft (2) to maintain the airtightness of the pump operating chamber (7). A suction port (13), an exhaust port (14) and an oil supply port (15) are provided in said housing (5) and connected to a vacuum tank (or a pressure accumulating portion of a master cylinder), an oil pan and an oil pump respectively, none of which are shown.
A rotor (16) of the generator is fixed to the shaft (2) and a stator (17) holds an armature winding therefor. A front bracket (18) is provided and together with the rear bracket (1) constitutes the outer frame of the electric generator and a bearing (19) is fixed to this front bracket (18) and rotatably journals the shaft (2). A pulley (20) is fixed to the shaft (2) and is driven by a belt, not shown, from the engine.
The operation will now be described:
First with respect to the vacuum pump, when the rotation of the engine is transmitted to the pulley (2) by a belt to rotate the shaft (2) in the direction of the arrow, the vanes (9) slide outward due to centrifugal force on the vanes and the outer ends slide along the inner wall of the housing (5) performing a pumping operation to suck air from within the vacuum tank (or the pressure accumulating portion of the master cylinder) and exhaust it through the exhaust port (14). Also oil supplied to the interior of the housing (5) through the oil supply port (15) effects the lubrication of the sliding surfaces of the vanes (9) and the rotor (4) and is exhausted to the oil pan through the exhaust port (14).
With respect to the electric generator, an alternating current is induced on the stator by the magnetic field generated from the rotor (16) during the rotation of the shaft (2). This alternating current is rectified to a direct current which flows into a charging circuit for the motor vehicle.
The electric generator for motor vehicles is generally belt-driven by the engine at a speed of rotation equal to about twice that of the engine in view of the power generation characteristic thereof. The vacuum pump directly connected to the generator also rotates at the same speed as the generator. For this reason, it is operates with abrupt acceleration and deceleration from a range of low speed of rotation (about 1000 rpm) to a range of high speed rotation (about 12000 rpm) and also the vacuum pump is continually being operated during the operation of the engine. Thus the components constituting the vacuum pump have previously been required to have durability and shock resistance so as to be able to rotate high rotation speeds and provide long service, resulting in an expensive device. Also since the electric generator is driven through the belt there has been the disadvantage that a vacuum can not be obtained when the belt is broken and the vacuum pump is stopped.